Q2 from M101 final exam

q2.js

// requires
var MongoClient = require('mongodb').MongoClient;

// mongodb uri
var uri = 'mongodb://localhost:27017/enron';

MongoClient.connect(uri, function(err, db) {
  console.log('Connecting to the db...');
    if (err) {
      console.log('Error during connection. Aborting.');
		process.exit(1);
	}
    console.log('Connected');
	db.collection('messages', function(err,collection) {
		
		collection.aggregate([
          { $match: {'headers.From':{$in:['[email protected]','[email protected]','[email protected]','[email protected]']}}}
          ,{ $project: {'from':'$headers.From','to':'$headers.To'}}
          ,{ $unwind : '$to' }
          ,{ $group : {
        	  _id: {from: '$from', to: '$to'},
        	  count: {$sum:1}
          	}
          }
          ,{ $sort: {count:1}}
        ], 
        
		function(err, result) {
              console.log(result);
          		db.close();
          });
	});

});